Re: [Trans] Precertificate format

"Hill, Brad" <bhill@paypal.com> Mon, 08 September 2014 23:46 UTC

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From: "Hill, Brad" <bhill@paypal.com>
To: Stephen Kent <kent@bbn.com>
Thread-Topic: [Trans] Precertificate format
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Date: Mon, 8 Sep 2014 23:45:57 +0000
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Subject: Re: [Trans] Precertificate format
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> I suggest that the CT designers list which data items from a cert that is being
> logged need to be in the SCT request, and why each item has to be present. Maybe that
> will show us how to avoid the concern that I and others have raised. It would also
> provide us with a starting point for the format of a new data structure for the SCT
> request, and the set of data that is input to the SCT hash computation.

The serial number needs to be part of the logged proof because that is the key on which existing revocation mechanisms operate.  Transparently identifying that a certificate has been issued incorrectly is of little utility unless that certificate can be revoked.

The alternatives are revoking the issuing CA on any leaf mis-issuance or inventing alternate revocation mechanisms. 

The latter may be less of an obstacle than it appears since the major implementers of CT are also in the process of inventing and deploying their own (currently) proprietary revocation systems alongside CT.

Nevertheless, one would need something stable to uniquely identify the certificate for these purposes, which ends up looking a lot like a serial number however you slice it.  (You can't use a cryptograhpic hash of the final cert for this, either, because that would require a preimage in the log.)

-Brad Hill